1. Field of the Invention
The present invention relates to a door weather strip, and more particularly, to a door weather strip for attachment to a periphery of a door of a motor vehicle.
2. Description of Related Art
A door weather strip is continuously attached to a periphery of a door of a motor vehicle. When the door is closed, a tubular seal portion of the door weather strip contacts and presses a door opening portion of a vehicle body to effect a seal between the door and vehicle body. As illustrated in FIG. 1, a door weather strip W includes an extruded member WA and corner member C1. The corner member C1 is formed by molding to connect longitudinal ends of the extruded member WA, and attached to a right-angled or slightly acute angled corner of a doorframe. Another corner C2 of the door weather strip W has been normally formed by bending an extruded member. If such corner C2 has a great curvature, it has been also formed by molding, similarly to the corner member C1. The extruded member WA of the door weather strip W has been normally composed of a foamed ethylene propylene diene terpolymer rubber (EFDM rubber).
Recently, thermoplastic olefin elastomer (TPO) has been used as glass runs for attachment along an inner periphery of the doorframe, or the like. TPO is advantageous over EPDM rubber, because TPO has a good elasticity and weather resistance approximately equal to those of EPDM rubber, does not require vulcanizing, and enables recycling of scraps thereof.
Foamed TPO has been used as a sealing member. The sealing member of foamed TPO, however, is not so preferable in its appearance and sealing properties, and consequently, has been only used in a limited use such as the sealing member around an engine of a motor vehicle.
The sealing member of foamed TPO has been produced by extruding a material containing TPO as a base, into which water as a foaming agent is mixed, with an extruder. The extruding temperature normally ranges from 140xc2x0 C. to 250xc2x0 C. In this extruding temperature range, the water mixed in the material is vaporized, but resultant water vapor is sealed within the material while the material passes a cylinder of the extruder. When the material comes out of an extruder, the pressure which has been applied to the water vapor within the material is reduced, and the water vapor is released to obtain foamed TPO.
The foamed TPO thus obtained, however, has a cell diameter as large as 100 to about 200 xcexcm, and consequently has rough surfaces. So, the appearance thereof is not suited to the member exposed to external view. In addition, this foamed TPO cannot effect good sealing properties, because of the large cell diameter thereof. When this foamed TPO is curved along the corner C2 or front and rear lower corners of the door panel, it would be undesirably distorted so as not to confirm to these corners of the door. Consequently, this foamed TPO is difficult to use as the door weather strip.
Accordingly, it is an object of the present invention to provide a door weather strip composed of a foamed TPO, which has excellent sealing properties, presents a good appearance, and is capable of being favorably attached to a vehicle door.
With the door weather strip of the present invention, which is to be attached to the periphery of a vehicle door, the extruded member is composed of a foamed TPO having an average cell diameter of 30 to 70 xcexcm, and an expansion ratio of 150 to 250%. The door weather strip composed of a foamed TPO of which the average cell diameter and expansion ratio are thus adjusted has smooth surfaces, and exhibits good sealing properties and good work efficiency in attaching.
The foamed TPO for use as the door weather strip is prepared by chemical foaming with a chemical foaming agent.